1. Field of the Invention
The present invention relates to pressure welders and has specific reference to a machine for pressure welding workpieces with an arc moving in a magnetic field.
2. Description of the Related Art
An invariably high quality of the welded joint combined with a high process productivity is a specific problem encountered in joining small-diameter pipes which cannot be revolved during the welding operation as this is the case in laying pipelines. At present, small-diameter pipes are joined mostly by manual welding, using coated electrodes or gas shields. The quality of the welded joint greatly depends in this case on the welder's skill, quality of the material and the conditions of welding.
To eliminate the disadvantages inherent in manual arc welding, micorprocessor-controlled orbital welders are sometimes employed. They quickly produce quality welds but add to the cost of the equipment, need skilled attendants and impose limitations on the environmental conditions (temperature, humidity and dust content of the atmosphere).
Small-diameter pipes and workpieces of intricate shape and small size are joined by welding machines employing an arc displacing in a magnetic field. The weld quality is high in this case but the machine itself is bulky and can be used in the shop only.
So, widely known is a pressure arc welder the arc whereof revolves in a magnetic field (Magnet-schweissen process advertised by KUKA Co. of FRG). The welder is designed for operation in the shop. It has a bedframe with clamping means of the chuck type which are mounted on guides and actuated by upsetting hydraulic cylinders. The bedframe gives support to hydraulic pumps, controls, positioners for loading and unloading the workpieces automatically and other equipment.
This machine is designed for specific applications such as, e.g. the fabrication of cardan shafts, clamps and other parts of intricate shape.
Also known in the art is a pressure welder with the arc revolving in a magnetic field (MBL--Schweistechnik Gerate, Vorrichtungen. Anwendungsbeispiele, N. 126, S. 7) which has two clamping means, a static one and a mobile one displacing in the axial direction, supported on a bedframe by guides. Each clamping means is provided in the form of two contact jaws one of which can displace radially for loading and unloading the workpieces.
Being installed in the shop, this machine can weld both long and small pieces. But its dimensions prevent field application.
Suitable for field application is a known pressure welder the arc whereof for heating the workpieces displaces in a magnetic field (SU; A; No. 1,207,684). The welder incorporates two clamping means for holding fast the workpieces which each have a holding-down plate hinged to a base and fitted with a means of displacing relative thereto and a clamping hydraulic cylinder a body of which is fitted to the base and a piston rod of which is hinged to tierods attached whereto is a holding-down roller located, on a side of the holding-down plate opposite to that where the hinged joint between the holding-down plate and the base is found, so as to interact with the holding-down plate in clamping the workpieces before welding; two upsetting hydraulic cylinders attached to a base of the static first clamping means whereas the second clamping means is mounted with its base on rods attached to the upsetting hydraulic cylinders at their ends with provision for reciprocating back and forth; and two means of setting a gap between the end faces of the workpieces which are movably linked to the upsetting hydraulic cylinders.
The rods mounted whereon as the second clamping means are cantilevers which deprive the structure of adequate stiffness. Significant tensile loads coming into play when long pieces are being welded bring about misalignment of the workpieces held fast in the clamping means. Therefore, the welded joint may not meet the specified requirements.
In the known machine each means of displacing the holding-down plate relative to the base consists of a handle, attached to the holding-down roller, and a first pulley linked by a cable to a second pulley which is fitted to the holding-down plate at the hinged joint thereof with the base. The holding-down plate is raised and lowered by the attendant who sets the holding-down roller into motion integrally with the tierods by operating the handle so that the first pulley revolves, winding or unwinding the cable.
This is a tiresome and inefficient job, and the cable interconnecting the two pulleys gets rapidly damaged so that the machine must be shut down for repair.
Each means of setting up a gap between the end faces of the workpieces being welded in the machine is essentially an adjustable stop and a spring-loaded sleeve which is operatively connected with the piston rod of the hydraulic cylinder and interacts with the body.
For setting up a gap between the ends of the workpieces to be joined by welding, fluid is fed under low pressure into the piston-rod end of the upsetting cylinder so that the piston displaces until the spring-loaded sleeve comes abutting against the cylinder body. Next, fluid is admitted into the same cylinder end under high pressure, causing the piston to displace further so as to compress the spring and shift the second clamping means into an appropriate position in which the piston rod comes abutting against the adjustable stop controlling the gap between the workpieces.
However, this arrangement fails to maintain an accurate gap between the end faces of the workpieces, for the pressure the piston is exposed to depends on the fluid pressure and this may vary in operation. An alteration of the gap may lead to a short circuit or may extinguish the arc moving therein. This has an adverse effect on weld quality.